: Cardiac remodeling plays an important role in the development of heart failure. Using oligonucleotide micro arrays, our lab has shown that the sarcomeric protein myomesin is up regulated and the cytoskeletal protein SLIM 1 down-regulated in failing compared to non-failing human hearts. Neither nether subcellular localization nor the function of myomesin or SLIM 1 in the human myocardium is known. The goal of these studies is to investigate the functional role of myomesin and SLIM 1 and the effect of altered expression in the failing heart. Under Specific Aim 1, the sub cellular localization of both proteins in failing and non-failing hearts will be investigated using immunohistochemistry and confocal microscopy. In Specific Aim 2, we will study the functional implications for altered expression of both genes. This will be achieved by manipulating the expression levels of myomesin or SLIM 1 in rat cardiac myocytes to mimic the changes that occur in the failing hearts using a recombinant adenoviral system. The structural effects of altered expressions of either gene will be examined using immunohistochemistry, in combination with confocal and electron microscopy. The functional effects will be investigated by measuring intracellular Ca2+ transients and cell shortening in rat adult cardiac myocytes over-expressing myomesin or with reduced expression of SLIM 1. In Specific Aim 3, to further elucidate the physiologic function of SLIM 1 and myomesin in the heart, proteins that interact with SLIM 1 or myomesin will be identified using functional proteomics (immunoprecipitation, 2-D electrophoresis, mass spectrometry, Western blot and affinity pull-down assay).